It is generally known that undesirable emissions of internal combustion engines may be significantly reduced by passing the engine exhaust gas through catalytic converters. When conventional converters are at light-off temperatures, such as temperatures above 350 degrees Celsius, exothermic reactions occur therein, resulting in efficient reduction of engine emissions. Converter temperature may be elevated to light-off temperature from latent exhaust gas heat. On cold start, a converter heated with latent exhaust gas heat may, under normal engine warm-up conditions, require 75 seconds or more to reach its light-off temperature.
Additional heat sources have been proposed for more rapid heating of the converter, so that efficient conversion of undesirable exhaust gas constituents may begin earlier after engine cold start. For instance, electrically heated converters have been proposed, in which electrical energy is selectively applied to a device that converts the electrical energy to thermal energy, which is made available to the converter. The efficiency of such heating systems requires that substantial electrical energy be expended before any significant emission reductions may be provided.
Alternatively, burner systems have been proposed for rapid heating of the converter. An example of such systems is provided in copending application U.S. Ser. No. 07/936467, filed Aug. 28, 1992, entitled "Exhaust Burner Catalyst Preheater," assigned to the assignee of this application. Such systems attempt to ignite an air/fuel mixture at a point upstream of the converter, whereby the released combustion energy operates to rapidly increase converter temperature. Although not suffering from the drawbacks of electrically heated units, such systems require coordinated control of a fuel input, an air input, and ignition, to ensure that the air/fuel mixture ignites as soon as possible at engine start-up, and that once lit, the burner expediently heats the catalytic converter to its light-off temperature.